1. Field of the Invention
The invention relates to a fuel-metering device according to the preamble of claim 1/3.
2. Description of the Related Art
Fuel-metering devices of this type are typically used as diaphragm carburettors for internal combustion engines. In the case of a diaphragm carburettor, a negative pressure produced during the intake procedure in an intake channel or a crank chamber serves to displace a movable diaphragm, thus causing a fuel stop to open and fresh fuel to flow into a fuel chamber. From the fuel chamber, the fuel flows via control devices and nozzles, which are known per se, into the intake channel where it is mixed with air also flowing in and finally is guided as a fuel-air mixture into a combustion chamber. In addition to other specific variables of the carburettor, the deflection of the diaphragm determines the quantity of fuel delivered in each case. The engine speed and the quantity of fuel delivered are approximately in proportion, since at a high engine speed a substantial quantity of fuel is taken in for each unit of time, whereas at a low engine speed and a correspondingly reduced number of strokes a smaller amount of flow flows.
DE 199 13 073 C2 discloses a fuel-metering device, wherein the position and/or the mobility of the movable element which is formed e.g. by a diaphragm can be influenced by an active control element, the controller of which is coupled to an ignition device of an internal combustion engine. In this way, where an ignition pulse is omitted, it is possible to reduce or even completely prevent excess fuel from being supplied into the intake channel of the internal combustion engine.
During the operation of internal combustion engines, to which the fuel-air mixture is supplied via a carburettor, the stoichiometrically correct composition of the fuel-air mixture is an important prerequisite for complete combustion, optimum engine performance and beneficial exhaust gas behaviour of the engine.
The concentration of oxygen per volume percentage of air is generally dependent upon the respective altitude, at which an internal combustion engine is utilised, wherein the oxygen concentration decreases at relatively high altitudes. Accordingly, the performance of the internal combustion engine during usage at relatively high altitudes is diminished owing to the reduced oxygen concentration and a deviation from the stoichiometrically correct composition of the fuel-air mixture which this causes. This makes it necessary to readjust the carburettor to adapt to the different altitude, in order to restore the optimum fuel-air ratio to be supplied to the internal combustion engine.
In this connection, reference may be made to documents DE-A-199.13.073 and DE-36.21.497.